This application relates to imagable implantable brachytherapy devices, and methods of use thereof.
Radioactive seed therapy, commonly referred to as brachytherapy, is an established technique for treating various medical conditions, most notably prostate cancer. In a typical application of brachytherapy for treating prostate cancer, about 50-150 small seeds containing a radioisotope that emits a relatively short-acting type of radiation are surgically implanted in the diseased tissue. Because the seeds are localized near the diseased tissue, the radiation they emit is thereby concentrated on the cancerous cells and not on distantly located healthy tissue. In this respect, brachytherapy is advantageous over conventional external beam radiation.
A number of devices have been employed to implant radioactive seeds into tissues. See, e.g., U.S. Pat. No. 2,269,963 to Wappler; U.S. Pat. No. 4,402,308 to Scott; U.S. Pat. No. 5,860,909 to Mick; and U.S. Pat. No. 6,007,474 to Rydell. In a typical protocol for treating prostate cancer, an implantation device having a specialized needle is inserted through the skin between the rectum and scrotum into the prostate to deliver radioactive seeds to the prostate. The needle can be repositioned or a new needle used for other sites in the prostate where seeds are to be implanted. Typically, 20-40 needles are used to deliver between about 50-150 seeds per prostate. A rectal ultrasound probe is used to track the position of the needles. Once the end of a given needle is positioned in a desired location, a seed is forced down the bore of the needle so that it becomes lodged at that location.
As the seeds are implanted in the prostate as desired, the needles are removed from the patient. Over the ensuing several months the radiation emitted from the seeds kills the cancerous cells. Surgical removal of the seeds is usually not necessary because the type of radioisotope generally used decays over the several month period so that very little radiation is emitted from the seeds after this time. Currently marketed radioactive seeds take the form of a capsule encapsulating a radioisotope. See, e.g., Symmetra® I-125 (Bebig GmbH, Germany); IoGold™ I-125 and IoGold™ Pd-103 (North American Scientific, Inc., Chatsworth, Calif.); Best® I-125 and Best® Pd-103 (Best Industries, Springfield, Va.); Brachyseed® I-125 (Draximage, Inc., Canada); Intersource® Pd-103 (International Brachytherapy, Belgium); Oncoseed® I-125 (Nycomed Amersham, UK); STM 1250 I-125 (Sourcetech Medical, Carol Stream, Ill.); Pharmaseed I-125 (Syncor, Woodland Hills, Calif.); Prostaseed™ I-125 (Urocor, Oklahoma City, Okla.); and I-Plant® I-125 (Implant Sciences Corporation, Wakefield, Mass.). The capsule of these seeds is made of a biocompatible substance such as titanium or stainless steel, and is tightly sealed to prevent leaching of the radioisotope. The capsule is sized to fit down the bore of one of the needles used in the implantation device. Since most such needles are about 18 gauge, the capsule typically has a diameter of about 0.8 mm and a length of about 4.5 mm.
The two radioisotopes most commonly used in prostate brachytherapy seeds are iodine (I-125) and palladium (Pd-103). Both emit low energy irradiation and have half-life characteristics ideal for treating tumors. For example, I-125 seeds decay at a rate of 50% every 60 days, so that at typical starting doses their radioactivity is almost exhausted after ten months. Pd-103 seeds decay even more quickly, losing half their energy every 17 days so that they are nearly inert after only 3 months.
Radioactive brachytherapy seeds may also contain other components. For example, to assist in tracking their proper placement using standard X-ray imaging techniques, seeds may contain a radiopaque marker. Markers are typically made of high atomic number (i.e., “high Z”) elements or alloys or mixtures containing such elements. Examples of these include platinum, iridium, rhenium, gold, tantalum, lead, bismuth alloys, indium alloys, solder or other alloys with low melting points, tungsten, and silver. Many radiopaque markers are currently being marketed. Examples include platinum/iridium markers (Draximage, Inc. and International Brachytherapy), gold rods (Bebig GmbH), gold/copper alloy markers (North American Scientific), palladium rods (Syncor), tungsten markers (Best Industries), silver rods (Nycomed Amersham), silver spheres (International Isotopes Inc. and Urocor), and silver wire (Implant Sciences Corp.). Other radiopaque markers include polymers impregnated with various substances (see, e.g., U.S. Pat. No. 6,077,880).
A number of different U.S. patents disclose technology relating to brachytherapy. For example, U.S. Pat. No. 3,351,049 to Lawrence discloses the use of a low-energy X-ray-emitting interstitial implant as a brachytherapy source. In addition, U.S. Pat. No. 4,323,055 to Kubiatowicz; U.S. Pat. No. 4,702,228 to Russell; U.S. Pat. No. 4,891,165 to Suthanthiran; U.S. Pat. No. 5,405,309 to Carden; U.S. Pat. No. 5,713,828 to Coniglione; U.S. Pat. No. 5,997,463 to Cutrer; U.S. Pat. No. 6,066,083 to Slater; and U.S. Pat. No. 6,074,337 to Tucker disclose technologies relating to brachytherapy devices.
The seeds have also been utilized to treat other types of cancers, such as pancreas, liver, lung and brain. For technical reasons, other organ systems or tissues are not amenable to this type of permanent seed implantation. These include hollow viscera such as the urinary bladder, mobile/muscular viscera such as the base of tongue, and tissues where a cavity or tumor bed has been created as a result of resection, as in the breast. In hollow viscera, loose seeds cannot be reliably spaced out owing to a dearth of tissue and the associated risk of losing the seeds into the lumen or cavity of the organ. Likewise in mobile/muscular and irregularly shaped viscera such as the base of tongue, loose seeds cannot be spaced reliably, and strands of permanent seeds like those described in U.S. Pat. No. 4,754,745 to Horowitz or U.S. Pat. No. 5,322,499 to Liprie are still too inflexible to be used because of the metallic seeds that are embedded within them. Similarly, the wire coils described in U.S. Pat. No. 6,436,026 to Sioshansi, although flexible, are not meant to be implanted permanently and require a means of afterloading and removal.
The situation in breast cancer is similar to that of a hollow organ, whereby loose seeds are difficult to space properly, and may fall into the resection cavity, thus spoiling the dosimetry plan. Despite U.S. Patent application No. 20020087078 by Cox which describes the insertion of a radioactive seed into a breast with cancer, the seed is placed inside the actual breast cancer and is removed along with the tumor at the time of the cancer surgery. Therefore, in this instance, the radioactive seed is not meant to serve a therapeutic purpose. Breast tissue is also similar to the base of tongue or other mobile organs since the breast may be very generous and supple, conforming to forces of gravity or pressure. In fact, for these reasons, metallic seeds are not currently used for permanent therapeutic implantation into a breast.
In each of the above circumstances where use of permanent seeds is not desirable, temporary implants are generally used. This is accomplished via placement of afterloading devices such as the Henschke applicator for cervix cancer, hairpin needles for the base of tongue, and silastic catheters for breast cancer. Once the respective applicators have been placed, radioactive sources are loaded and remain indwelling for a prescribed finite period, usually hours to days. The sources and afterloading devices are then completely removed.
Disadvantages of these temporary systems are that patients often must stay in the hospital for the entire time that low dose rate sources are indwelling, or between radiotherapy fractions or sessions if high dose rate sources are used. In the case of afterloading catheters, the catheters are sutured in place for several days, causing acute pain, swelling, and possible infection or scarring. In the case of base of tongue implants, patients frequently require temporary tracheostomies to keep their airway open while the hairpin needles remain in place. In one new temporary high dose rate system by Proxima Therapeutics®, surgical placement of a balloon catheter is performed on the breast. The device has a catheter leading from the balloon in the tumor bed to the skin to provide ingress and egress for the temporary brachytherapy source. The balloon is deflated at the conclusion of several days of brachytherapy sessions, and is pulled out of the breast by hand.
It is an object of the present invention to provide biodegradable strands or other structures that are flexible and permanently implantable.
It is another object of the present invention to provide biodegradable strands or other structures that are flexible and implantable.
It is still another object of the present invention to provide non-polymeric biodegradable implantable seeds and a means for readily imaging implanted seeds.
It is also an object of the present invention to provide brachytherapy seeds and strands which can be used for other purposes, for example, drug delivery.